Encapsulated semiconductor device with a metallic base plate

Abstract

A semiconductor device comprising a metallic base plate whose side surfaces are formed with cut-away portions having circular arc-shaped parts, a semiconductor element which is connected to the surface of the metallic base plate, and a resin which lies in contact with the cut-away portions and which seals the semiconductor element.

We claim: 
     
       1. A resin-molded semiconductor device comprising: a metallic base plate which includes a first sheet portion having a first pair of opposing sides, said sides defining a width of said first sheet portion, and a second sheet portion extending from another side of said first sheet portion which is located in a direction which crosses said first pair of sides of said first sheet portion, said second sheet portion having a second pair of opposing sides extending in the same direction as that of said first pair of opposing sides, the width of said second portion defined by said second pair of opposing sides being less than the corresponding width of said first sheet portion, said second sheet portion adjoining in a middle part of said another side so as to be line-symmetric with respect to a straight line to said another side;   a pair of arcuate recess portions respectively provided in said first and second sheet portions in an area where said another side and the respective second sides intersect each other;   a semiconductor element fixed to said second sheet portion;   a plastic package which covers said semiconductor element and said second sheet portion, but which does not cover said first sheet portion; and   mounting means provided in said first sheet portion for mounting said first sheet portion on an external heat sink.   
     
     
       2. A resin-molded semiconductor device according to claim 1, wherein said mounting means comprises a pair of holes for inserting mounting screws therein, said pair of holes being respectively formed in opposite extended parts of corresponding wide portions, each of which projects more than the width of the second sheet portion. 
     
     
       3. A resin-molded semiconductor device comprising a metal plate having opposite side edges, each of which is stepped so that the plate has a wider portion and a narrower portion, both portions extending from one of said side edges to the other;   a semiconductor element mounted on the said narrower portion;   means on said wider portion for securing said device to a heat sink;   a recess in each of its said sides of said plate in the region of the step in the side, each said recess having an outline, as seen in the direction perpendicular to the plate, which at leat partly consists of a curve; and   a plastic material package which covers said semiconductor element and at least part of said narrower portion of the plate, so as to protect the element and fill the recesses, but not to cover said wider portion of the plate.   
     
     
       4. A semiconductor device according to claim 1, or 3, wherein each said recess, as seen in the direction perpendicular to the plate, has a keyhole shape, with a circular arc portion located inwardly of the plate with respect to a shank portion which has a diameter less than said circular arc portion. 
     
     
       5. A semiconductor device according to claim 3, wherein a pair of holes for securing screws are respectively formed in opposite extended parts of the wider portion, each of which opposite extended parts is projected more than the corresponding width of narrower portion and forms the step. 
     
     
       6. A resin-molded semiconductor device comprising: a metallic base plate which includes a first sheet portion having a first pair of opposing sides, said sides defining a width of said first sheet portion, and a second sheet portion extending from another side of said first sheet portion which is located in the direction which crosses said first pair of sides of said first sheet portion, said second sheet portion having a second pair of opposing sides extending in the same direction as that of said first pair of opposing sides, the width of said second portion defined by said second pair of opposing sides being less than the corresponding width of said first sheet portion, said second sheet portion adjoining a middle part of said another side so as to be line-symmetric with respect to a straight line to said another side;   a semiconductor element fixed to said second sheet portion;   a plastic package which covers said semiconductor element and said second sheet portion;   mounting means provided in said first sheet portion for mounting said first sheet portion on an external heat sink; and   a pair of arcuate recess portions respectively provided in said first and second sheet portions in an area where said another side and the respective second sides intersect each other to reduce stress induced on said plastic package by said mounting means in said first sheet portion by dispersing said stress to said plastic package along edges of said arcuate recess portions.   
     
     
       7. A resin-molded semiconductor device comprising: a metal plate having opposite side edges, each of which is stepped so that the plate has a wider portion and a narrower portion, both portions extending from one of said side edges to the other;   a semiconductor element mounted on the said narrower portion;   means on said wider portion for securing said device to a heat sink; and   a plastic material package which covers said semiconductor element and at least part of said narrower portion of the plate, so as to protect the element,   wherein said plate has a recess in each of its said sides in the region of the step in the side, each said recess having an outline, as seen in the direction perpendicular to the plate, which at least partly consists of a curve, to reduce stress induced on said plastic package by said securing means in said wider portion by dispersing said stress to said plastic package along edges of said curve.